Axial piston variable displacement hydraulic devices utilize a tiltable swashplate to control the displacement of pistons within a rotating cylinder block. One common type of tiltable swashplate is a cradle type swashplate which is supported at one end of the housing by a pair of laterally spaced arcuate roller bearings disposed between a convex arcuate surface on the swashplate and a concave seating surface in the housing. Each of the pair of roller bearings has a plurality of rolling elements and a bearing race locating the individual rollers of the bearing. In order to assure that the arcuate rolling bearings do not slip to an adverse position during operation, some of the hydraulic devices have a timing or locating arrangement extending between the swashplate and the housing and being connected to the cage of the cradle bearing. Other hydraulic devices have the cradle type swashplates supported by a pair of laterally spaced, anti-friction sleeve bearings disposed between the swashplate and the housing. Generally, the roller bearings are commonly used in the devices subjected to high pressures while the sleeve type of bearings are used in low pressure devices.
The cost of the roller bearings are generally several times more than the cost of sleeve bearings and the use of roller bearings on both sides of the devices may unduly add to the total cost of the unit. For example, it has been found that the bearing at one side of the pump is generally highly loaded during operation while the bearing at the other side is generally lightly loaded. More specifically, if the hydraulic device is a pump, the bearing at the discharge or outlet side is highly loaded while the bearing at the inlet side is lightly loaded. If the hydraulic device is a motor, the bearing at the inlet side is highly loaded while the bearing at the outlet side is lightly loaded.
In view of the above, it would be desirable as a cost saving measure to utilize a bearing arrangement in which a more expensive roller bearing is used only on the normally highly loaded side of the hydraulic device, while a less expensive sleeve type bearing is used on the normally lightly loaded side of the device.
The present invention is directed to overcoming one or more of the problems as set forth above.